V O L U M E 2 4 , N O . 1, J A N U A R Y 1 9 5 2
193 Temperature Compensation. Although the sample teniperature was maintained to 30" i.0.1"C. throughout the laboratory evaluation, the instrument recording bridge circuit is adaptable t o standard methods of temperature compensation. AL properly shunted resistance thermometer or thermistor could be used in series with the phototube track slide-wire. The problem is complicated by the nonlinear relationship between resistance and refractive index, and therefore a series of compensators x-ould b e necessary if the full range of the refractometer should be used. If the instrument should be employed as a control device to maintain constant refractive index, compensation would be straightf0rLvai-d. CONCLUSIOS
The focusing cell refractometer provides a method for continuously recording the refractive index of transparent liquids. Limited transparent coating of the lens and predictable color changes should have no effect on operation. The experimental instrumeiit constructed will operate with a series of three properly designed cylindrical lenses over a range of 1.34 t o 1.56 with an accuracy of 10.0002.
Figure 5 .
Calibration Curve
model is 0.0002 in refractive index. Xs t h e noise is of n constant nature, the sensitivity of the iiistrument is approximately 0.0001. The sensitivity of any given instrument can be modified in someivhat the same manner as the range. Because, a s indicated in Equations 5 and 6, the sensitivity is inversely proportional t o the radius of curvature of the cylindrical lens, the sensitivity range is limited only by the limits of good lens design. X series of replaceable lens of equal refractive index and varying curvatures might be designed for an instrument t h a t is t o be operated through a limited refractive index range. The increase in sensitivity by this method nil1 result in a corresponding increase in accuracy.
LITERATURE ClTED
Barnes, R . B., t-.S.Patent 2,413,208 (Dec. 24, 1916). Barstow, 0. E.. Instrziinents. 23, 396 (1950). Cai,y, H.. -1gyiied Physics Corp., P a s a d e n a , Calif., Private Comtiiuiiication. .Jones. H. E., .islimnti, L. E . , and S t a h l y , E. E., = ~ N A L .CHEM.,21, 1479 !1949!.
Karrer. E.. and Om, R.S.,J . Optical SOC.Bm., 36, 42 (1946). Melville, H. TI-., 311d \J-atson, TI-. F., Trans. Faraday Soc., 44, 68 (1948).
Thomas, G. R.. O'Konski, C. T., a n d Hurd, C. D., Az.4~. CHEM., 22, 1221 (1950). Zaukelies, D., and Frost, A. A, Ibid., 21, 743 (1949). RECEIVEDN a y 4, 1951. Contribution from the Multiple fellowship on Synthetic Rubber Instrumentation of the Reconstruction Finance Corp., Office of Rubber Resen e.
Detection of Chromatographic Zones by Means of High Frequency Oscillators P. H. MONAGHAN', P. B. MOSELEY, T. S. BURKHALTER2, AND 0. A. NANCE Louisiunu S t a t e University, B a t o n Rouge, La. One of the obstacles to the extension of chromatography to a large number of applications lies in the difficulty of detecting the location and measuring the rate of motion of zones on the column. For this reason, the authors have adapted a heterodyne type of high frequency apparatus to the detection of chromatographic zones. Preliminary tests indicate that a wide variety of materials may be detected in this manner; the sensitivity in each case is deter-
T
HE detection of colorless zones on a chromatographic column
is a difficult problem, but one in which the chromatographer is vitally interested. Various investigators have located colorless zones by extruding the column and applying appropriate streak reagents or by driving the zones completely through the column and analyzing the filtrate. Claesson ( 2 )has devised a continuous, recording "filtrate analyzer," which depends upon measurements of the refractive index of the filtrate. 1
Present address, Humble Oil Co., Houston, Tex. Texas State College, Denton, Tex.
* Present address, North
mined by the electrical properties of the solutes, solvent, and column packing. A comparison of the measurements made with this instrument with those made by routine visual and chemical methods indicates that the results compare well within the experimental error of the customary methods. This instrument should increase the variety of compounds that may be studied by chromatography and provide a rapid and reproducible method.
Jensen and Parrack ( 3 ) described a high radio-frequency oscillator which could be used as a chemical titrator by placing the liquid sample inside the coil of the resonant tank circuit of the oscillator and measuring the variations in plate current produced by addition of titrant. Arditti a n d Heitzmann ( 1 ) modified Jensen's method by measuring the variations in grid current. T e s t and Burkhalter (6) used two matched high radio-frequency oscillators operating a t t h e same frequency. They measured frequency differences produced by introducing samples into the tank coil of one of the oscillators; the other oscillator served as the f r e
ANALYTICAL CHEMISTRY
194 quency reference, The frequency differenor between the “working oscillator” and the “reference oscillator” could then be interpreted in terms of the nature and composition of the chemical system under investigation. N a n c e , B u r k h a l t e r , a n d Monaghan ( 5 ) have modified the original method, placing the liquid samplc inside a
Gh r orna t o g r a p h ic Column
PI
24
zP3 0
U ).
33 9er
Condenser Plates
/ F I
n
0
2
PO 30 V O L U M E OF DEVELOPER, M L .
10
4
Figure 2. Audio
Aniline Acetone
C.
Phenol Ethyl alcohol Methanol
E.
p 2.9
-
I
I
I
I 51
Se\eral \dsorpti\es Run on Single CO~IIITIII
A. B. L).
Frequency
I
40
1.
2.
Sample put on column Zone in plates
Developer, benzene
n
X
Figure 3. Separation of Nitrobenzene and Rlethaiiol Sample volume, 1 ml. Developer, benzene Column length, 90 mm.
s 9.8 3
a
p P.7 LL
-
I-
9m small rondenser (in parallel with the main tuniug condenser). This change leads to a major increase in sensitivity. This paper describes the results obtained when a portion of the chromatographic, - . column is placed between the plates of a capacitor in the tank circuit of a high radiofrequency oscillator.
2.6
-
2.5 r
9.4 0
APPARATUS
X block diagram of the apparatus used is shown in Figure 1. The chromatographic column was made from 9-mm. horosilicate glass tubing. A small condenser was made by attaching semicircular plates of aluminum foil or copper screen, 1 cm. in length, to the wdls of the column. This condenser was connected in parallel with the tank condenser of a Clapp oscillator operating in the vicinity of 5 megacycles. Th(, output of the oscillator was mixed with the output of a crystal oscillator and the resultant audio-frequency voltage wafi connected to the vertical amplifier of a cathode-ray oscilloscope. -4Hewlitt-Packard audio-oscillator was connected to the horizontal amplifier of the oscilloscope and the frequency difference between the radio-frequency oscillators was determined from the Lissajous figures. The column was packed with adsorbent and, when necessary, prewashed with solvent before frequency measurements Tvere rcJcordrd. This method of detection has been applied to both dilute solution chromatography and displacement development. Figure 2
5
10 15 V O L U M E OF DEVELOPER, M L .
Table I.
P5
Comparison of R Value Determinations
Compound .Iniline Acetone Phenol
?Jethano1
PO
Ethyl alcohol
K , Oscillator
R , Streah Test
0.74 0.74 0.69 0 27
0.76 0 71 0.73 0.24 0.40
0 43
s h o i ~ sthe results obtained when samples of five different conipounds TI ere run through a single column. The adsorbent was Florisil, prewashed R ith 3 column volumes of tmmenc. The column length v a s 115 mm measured from the eondenser plates t o the top of the packing. The samples used mere 1-ml portions of 0.5 M solutions of the adsorptives in t~rnzrne. The first sample was put on the column and folloaed by pure developer; this procedure was repeated for each succeqsive sample. Bfter the last sample was on the column, developri \vas nddrd until all samplrs had pasped between the capacitor
V O L U M E 24, N O . 1, J A N U A R Y 1 9 5 2
195
To check the validity of the zone indications given by the instrument, the R values of 3.4 the compounds were calculated and checked against the R values determined by extruding the column and locating the zone by means of 7 3.3 3.3 streak tests. The parameter, R, has been defined by LeRosen ( 4 ) as the ratio of the rate X 2. 3.2 of movement of t,he leading edge of a zone to U the rate of movement oi the developing sol33 vent. The agreement bet.ween the R values, 9 3.1 as shown in Table I , is not exact but proves E conclusively that the zone indicated by the + oscillator is the same as that indicated by the 3.0 m m 3.0 streak test. Refinements of experimental procedures should improve the quantitatiye com2.9 parison of the txTo methods. The separation of a misture of nitrobenzene and methanol, in benzene solution, on a P.8 I I I I I J Florisil column is presented in Figure 3. The 0 P 4 6 8 10 12 maximum a t 5 ml. is due to nitrobenzene and V O L U M E OF DEVELOPER, M L . that a t 15 ml. is due to methanol. Figure 4 Figure 4. Incomplete Separation of Acetone and Nitrobenzene illustrates the effect obtained by insufficient Sample volume, 1 ml. separation of a mixture of nitrobenzene and Developer, benzene acetone. The nitrobenzene zone start,s to Column length, 107 mm. move out of the condenser area as the leading edge of the acetone zone moves in; the result of this phenomenon is a hump with a long P.1 trailing edge. The procedure of displacement development 1.P involves the introduction of a mixture into the column and the use of a developer which is more strongly adsorbed than any material in 7 1.0 the mixture. Thus, the components in the z sample group themselves into zones in the X order of increasing strength of adsorption and z 0.8 U all move through the column a t a rate deterZ mined by the developing solvent. Figure 5 shows the results obtained when 9 0.6 E 3 ml. of a solution containing 33.3y0 each of benzene, diethyl ether, and petroleum ether B y 0.4 were placed on a dry Florisil column and developed with 9570 ethyl alcohol. The difference Benzene between successive readings of the beat fre0.P quencj- was plotted against volume of solvent placed in the column and the plot of the data - . I I I shows three definite peaks corresponding to the 0 0 P 4 6 8 10 12 14 16 18 PO three components in the mixture. The width V O L U M E OF DEVELOPER, ML. of each of these peaks corresponds to approximately 1 nil., a result that is consistent with the Figure 5. Displacement Development of the original mixture and the fact composition 33.370 petroleum ether, 33.370 benzene, 33.39’0 diethyl ether Sample composition. Sample volume, 3 ml. Developer, ethyl alcohol Column length, 237 mm. that the volume of the sample was 3 ml. The authors believe that the sensitivity of the instrument can be imm-oved sufficiently to plates. The u orking oscillator was adjusted to operate below the permit the detection of zones of lower concentration. The time crystal, in order that passage of the samples through the conrequired for zone detection could be reduced by using a detached denser plates might produce an increase in the measured frecapacitor and by moving the column between its plates. Work quency difference; the effect of all materials having a dielectric is now directed toward effecting these improvements. constant higher than that of benzene was to lower the frequency of the working oscillator.
-
-
-
-
d
-
L
s
7
An inspection of the graph shows that the zones are indicated by a definite increase in the difference fre4uency; the difference frequency drops back to its original value very quickly after the passage of the aniline and phenol zones but compounds like acetone and methanol apparently leave a portion of the material on the column and raise the background level. This was to be expected, as previous studies by conventional methods had shown that columns washed with acetone retained, over the whole length of the column, a small amount of acetone which could not readily be washed away with benzene.
LITERATURE CITED
(1) Arditti, R., and Heitzmann, P., Compt. l e n d . , 229, 44-6 (1949). (2) CIaesson, Stig, Ann. iV. 1’. Acad. Sci., 49, 183-203 (1948). (3) Jensen, F. E‘.. and Parrack, 8.L., IND.ENG.CHEM.,ANAL.ED., 18, 595-9 (1946).
LeRosen, A. L., J . Am. Chem. Soc., 64, 1905-7 (1942). Nance, 0. A., Burkhalter, T. S., and Monaghan, P. H., SAL. CHEM.,24,214 (1952). (6) Kest, P. W., Burkhalter, T. S., and Broussard, L., Ibid., 22, (4) (5)
469 (1950). RECEIVED J u n e 28. 19.50
